After a hydrocarbon deposit has been drilled, a production casing is installed, and then perforated at desired areas to allow hydrocarbons in the earth to enter the casing and be extracted upwardly to the surface. The perforated casing prevents the well from eroding or deteriorating, as well as allows the hydrocarbon to pool therein so that the minerals can be pumped, or otherwise extracted.
Production casings are generally perforated with groups of holes encircling the casing, such groups being located along the axis of the riser where hydrocarbon formations are expected to be found. During exploration and drilling, the location and depth of such formations can be accurately determined. The production characteristics of the subterranean formation may change over time, necessitating the closing off of the hydrocarbon inflow of certain formation levels. For example, it is often desirable to block off perforated casing areas near formation levels where there is an influx of sand or other contaminating material. Also, the hydrocarbon material at such levels may run out and be replaced with water.
In order to close off such areas or zones of the production casing and avoid the influx of such contamination, packing equipment is utilized. A packer is essentially apparatus which can be installed at any point within the casing for shutting off the hydrocarbon flow therein, except through a crossover passageway which allows hydrocarbons from lower formations to pass through the blocked off area. In order to isolate a perforated zone, an upper and lower packer are utilized for providing a seal to the production casing above and below the perforated zone. A crossover extends through the packers and is sealed thereto In this manner, the perforated zone of the casing is isolated from the remaining part of the production casing, thereby allowing hydrocarbons to be produced from below the packers, forced through the crossover, and to surface equipment.
Isolation packers are well known in the art for accomplishing the noted functions. U.S. Pat. No. 4,401,158, for example illustrates a multi-zone gravel packer for isolating desired zones of a production casing and packing the same with gravel. While the packer of the noted patent is effective to install several levels of packers with only a single trip of the drill string, there are no provisions for removing the packers from the casing, or for moving the packers from one location in the casing to another. Packers constructed according to the noted patent have an inherent disadvantage, in that in order to retrieve the lower hydraulically set packer, the tubing string must be disconnected from the uppermost mechanically set packer, and a shifting tool inserted for releasing the lower packer.
Mechanically set packers utilizing slips can also be employed as both upper and lower packers for isolating perforated zones of a production casing. A retrievable packer utilizing slips is expensive due to the complexity thereof. Also, mechanically settable and releasable packers have a tendency to hang up in the casing perforations, thereby resulting in damage to the packer or to the well casing during removal of the packer.
Cup-type packers provide yet another alternative in isolating zones of a production riser. Cup-type packers are not expandable or retractable under an operator's control, and thus remain in continual contact with the inside surfaces of the production casing. Thus, when such cup-type packers are forcibly moved in the casing, such as during installation or removal, the cups become worn and often damaged when forced past the perforations or coupling joints of the casing. When such packers become excessively worn or torn, an undesired leakage of fluids may occur from one casing zone to another. Moreover, when employing cup-type packers, a quantity of fluid must be pushed by the cups in the same direction that the tubing string is moved, which fluid may be forced through the perforated zones back into the formation as the tubing string is pushed into the well, or fluid is slubbed from the casing as the tubing string is pulled from the well.
From the foregoing, it can be seen that a need exists for an improved packer which requires no slips, is hydraulically set and hydraulically released, and thus can be efficiently installed or removed from the production casing. An associated need exists for packing apparatus which is not unduly complicated, thus facilitating manufacture thereof and resulting in a cost effective and reliable product.